Atmospheric excitation of the Earth's annual wobble: 1980-1988

Global meteorological analyses from the European Centre for Medium Range Weather Forecasts are employed to compute the atmospheric excitation Ψ of the polar motion for the 9-year period of 1980-1988. Both the matter component Ψ(motion) are computed, the former with and without the oceanic inverted barometer (IB) effect. It is found that Ψ(motion) contributes significantly to the total excitation Ψ overall and nonnegligibly to the annual signal in Ψ, or the annual wobble excitation, in particular. Our results for the annual wobble excitation, in terms of the prograde component Ψ⁺ and the retrograde component Ψ^- for January 1, are Ψ⁺= (16.8 milliarc seconds (mas), -93°) and Ψ^-=(15.6 mas, -98°) with IB, and Ψ⁺=(17.3 mas, 101°) and Ψ^-=(28.1 mas, -112°) without IB. These results are within the (rather large) range of previous estimates. The IB effect has a small impact on Ψ⁺, whereas its impact on Ψ^- is considerable. The (better determined) prograde components Ψ⁺ are then compared with that observed from the Lageos satellite laser range data: (17.3 mas, -61°). Although the amplitudes are nearly equal, large phase discrepancies exist between the atmospheric and this observed value. The resolution of this discrepancy awaits a better knowledge of the seasonal angular momentum budget on the Earth's surface fluid elements.